Tire rubber compositions containing silica as a filler are often inferior to those containing carbon black in abrasion resistance and mechanical strength (tensile strength and elongation at break). In order to improve such properties, a method using a silane coupling agent and a method using microparticulate silica which has high reinforcing properties are known.
In the case of using a silane coupling agent, silica may not be sufficiently reacted with the silane coupling agent, and unreacted silica may remain poorly dispersed. Here, the reaction between the silane coupling agent and the silica can be promoted if the kneading temperature is increased. However, an excessive increase in the kneading temperature may cause an increase in Mooney viscosity, and thereby the processability may be deteriorated and rubber burning (scorching) may occur.
For solving the above problems, Patent Documents 1 and 2 disclose a tire (especially tread) rubber composition containing a silica (surface-treated silica) with its surface pretreated with a silane coupling agent. This rubber composition may improve properties such as abrasion resistance. However, the investigations by the present inventors show that the improvement is not sufficient, and there is room for improvement especially in the case of using a modified diene rubber that has been recently increasingly used for achieving low fuel consumption, in particular, a modified diene rubber having two or more modified groups in one molecule.    Patent Document 1: JP 3933207 B    Patent Document 2: JP 2001-11245 A